High-temperature reflective coating and method of making the same



1964 w. WESTERVELD ETAL 3,

COATING HIGH-TEMPERATURE REFLECTIVE AND METHOD OF MAKING THE SAME Filed Nov. 2. 1961 INVENTOR WILLEM WEST ERVELD JOHANNES FLIPSE BYRUDOLF M.K um K United States Patent 3,160,513 HIGH-TEMPERATURE REFLECTTVE (IQATHNG AND METHGD 6F MtAKlNG THE SAME Willem Westerveld, Johannes Fiipse, and Rudolf Maurits Kruiminir, all of Emmasingel, Eindhoven, Netherlands, assignors to North American Philips Company, lino, New York, N.Y., a corporation of Delaware Filed Nov. 2, 1961, Ser. No. 149,609 Claims priority, application Netherlands Nov. 19, 1960 2 Ciaims. (Cl. 11735) The invention relates to a method of applying aluminum by vaporisation to a support. The method according to the invention is particularly suitable for the manufacture of aluminum mirrors exposed to high temperatures.

Aluminum mirrors are frequently used in incandescent lamps.

When such a lamp burns, the temperature of the aluminum l-ayermay locally increase to about 350 C., at which value the reflection power decreases.

A particular type of incandescent lamp provided with an aluminum mirror is obtained by sealing a conical part of pressed glass provided with an aluminum mirror to a flat part of pressed glass. For a short time the sealing temperature amounts to about 800 C. Under these conditions the mirror of pure aluminum thus obtained is transparent at the points Where these high temperatures prevailed.

This phenomenon is probably to be attributed to recrystallisation in the layer.

The object of the invention is to provide a method of manufacturing aluminum mirrors which are free of this drawback.

It has been found that such aluminum mirrors can be obtained by using an alloy of aluminum and a small quantity of one or more of the metals of the iron group; iron, cobalt and nickel.

The layers obtained by using this alloy may be exposed to high temperatures for a long time without any appreciable change in the layer taking place.

For practical reasons use is preferably made of an alloy containing in total between 0.1 and 1% by weight of the said metals iron, cobalt and/or nickel. Below 0.1% by Weight the said effect is obtained to a much smaller extent and above 1% by weight difliculties arise, when the same source of heat, for example an incandescent helix of tungsten or molybdenum is employed for a long time to transfer by vaporisation repeatedly fresh quantities of the alloy. With the same temperature of the helix the vaporisation time required is then found to increase gradually. Probably, this eflect may be ascribed to the enrichment of the incandescent helix in the metal admixture of the alloy.

Patented Dec. 8, 1964 The method according to the invention will now be described more fully with reference to the accompanying drawing.

FIG. 1 is an elevation of the source of heat.

FIG. 2 is a sectional view of a mirror coating arrangement.

FIG. 3 is a sectional view of a lamp provided with an aluminum mirror according to the invention.

With the method according to the invention a suitable source of heat may, for example, be anincandescent helix of tungsten or molybdenum, designated by 1 in FIG. 1. A strip 2 of the alloy to be vaporized is inserted into the helix. The assembly may be arranged on a plate of suitable, insulating material, designated by 4 in FIG. 2. On the plate 4 is arranged a glass cone 3, which communicates at 5 with an exhaust pump. After adequate vacuum has been attained, for example between 10- and 10' mm. mercury, the incandescent helix is electrically heated to a temperature of about 2000 C. After approximately 10 seconds 15 mgs. of the alloy will provide a layer of about 1500 A. in thickness.

FIG. 3 is a sectional view of a finished lamp; reference numeral 6 designates the aluminum mirror, provided on the conical part 3 of the lamp; after the mirror has been applied, the Hat or spherical part 7 is sealed to the conical part. The mirror does not exhibit any visible change, when the aforesaid alloy is used. If pure aluminum (99.98%) is used, the edge of the mirror is transparent after the parts 3 and 7 have been sealed together.

What is claimed is:

1. A method of providing on a support a reflective coating capable of withstanding temperatures of at least 350 C. without loss of reflectivity comprising the stepof applying to the support a layer of an alloy consisting of about 99.0 to 99.9% by Weight of aluminum and about 0.1 to 1% by weight of a metal selected from the group consisting of iron, cobalt and nickel.

' 2. An object comprising a support and a reflective coating thereon capable of withstanding temperatures of at least 350 C. without loss of reflectivity, said coating being an alloy consisting of about 99.0 to 99.9% by weight of aluminum and about 0.1 to 1% by weight of a metal selected from the group consisting of iron, cobalt and nickel.

References Cited in the file of this patent UNITED STATES PATENTS 2,160,714 Biggs May 30, 1939 2,918,595 Cressman Dec. 22, 1959 FOREIGN PATENTS 492,928 Great Britain Sept. 29, 1938 

1. A METHOD OF PROVIDING ON A SUPPORT A REFLECTIVE COATING CAPABLE OF WITHSTANDING TEMPERATURES OF AT LEAST 350*C. WITHOUT LOSS OF RELECTIVITY COMPRISING THE STEP OF APPLYING TO THE SUPPORT A LAYER OF AN ALLOY CONSISTING OF ABOUT 99.0 TO 99.9% BY WEIGHT OF ALUMINUM AND ABOUT 0.1 TO 1% BY WEIGHT OF A METAL SELECTED FROM THE GROUP CONSISTING OF IRON, COBALT AND NICKEL. 